An empirical test of the 'predictability' hypothesis for the evolution of viviparity in reptiles

R. Shine*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

20 Citations (Scopus)


Viviparity (live-bearing) has evolved from oviparity (egg-laying) >100 times in reptile phylogeny, but the selective forces responsible remain unclear. Tinkle & Gibbons (1977) proposed that prolonged uterine retention of eggs (leading ultimately to viviparity) is favoured by natural selection when it allows the reproducing female to better predict the incubation conditions that will occur in alternative potential nest-sites, and hence select the optimal site in which to deposit her eggs. This ingenious hypothesis has never been tested empirically. Over a 7-year period, I monitored temperatures inside 124 natural nests of egg-laying scincid lizards at three different elevations in the Brindabella Range of south-eastern Australia. As a measure of thermal predictability, I used correlation coefficients from comparisons of temperatures early vs. later in incubation among nests within each site. Both the mean and standard deviation of nest temperatures were examined in this way for each week through incubation. I performed these calculations under two models: one where the female assesses nest temperatures at the time of oviposition only, and one where she monitors temperatures constantly from the usual oviposition date until the actual time of laying. These analyses falsified two major assumptions of the 'predictability' hypothesis. First, nest temperatures at higher elevations were no less predictable than were those at lower elevations; instead, predictability was high in all situations. Secondly, a longer delay before oviposition decreased rather than increased the predictability of thermal conditions during subsequent incubation. I conclude that critical assumptions of the 'predictability' hypothesis are not supported in this study system.

Original languageEnglish
Pages (from-to)553-560
Number of pages8
JournalJournal of Evolutionary Biology
Issue number4
Publication statusPublished - Jul 2002
Externally publishedYes


  • Adaptationist hypothesis
  • Australia
  • Bassiana duperreyi
  • Lizard
  • Natural selection
  • Nest temperatures
  • Scincidae
  • Uterine retention


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